Clutch assembly



April 17, 1956 Filed May l2, 1951 J. W. PALM CLUTCH ASSEMBLY 2 Sheets-Sheet l fTLz/erzlLof:

Jar/e5 ZU. Palm April 17, 1956 J'. w. PALM CLUTCH ASSEMBLY Filed May 12, 1951 2 Sheets-Sheet 2 United States Patent CLUTCH ASSEMBLY James W. Palm, Rockford, Ill., assignor to Borg-Warner Corporation, Chicago,flll., a corporation of Illinois Application May 12, -19'51,SerialNo. 226,069 14 ClmS. `(Cl. Y1`9'2Q89) The present-improvements relate'generally to clutches and'more particularly to clutchesjwliich are adapted for heavy duty where severeeserviceis required.

Clutches of above-mentioned typeare'usually provided with overcenter actuating Ameans and are installed in tractors and other "heavy vehicles, such as earthurnoving machines and the like. During the useof theselrnachines, there is frequent engagement `and disengagement of the clutch while itis rotating at high speeds and this results in the generation of considerable heat in the clutch assembly. Heating of the parts is injurious to the clutch mem-` bers because they tendto warp, and it has been'foundthat some of the parts lare damaged to such Van extent that they require replacement which causes delay in coinpleting the task being performed.

When overcenter engaging and disengaging mechanism is employed in these clutch assemblies, some of the component parts `of the overcenter mechanism when ro rating at high idling speeds andthe clutch has `been disengaged these `overcenter parts frequently respond to centrifugal forces with the result that these parts tend to eiect unintentional engagement of the clutch driving and driven plates.` j

`lt is desirable inclutches of this `character to Aprovide yieldable means between the pressure applying mechanism or toggle devices and the shiftable pressure plate so as to exert Vspring force against these toggle devices to hold them in overcenter position when the clutch has been engaged. The yieldable means preferably takes the form of a spring bar located between the pressure plate and the overcenter toggle mechanism, so'that, when the friction surfaces of the clutch driving and driven members wear, the pressure plate is permitted to follow up with a sutlicient amount of pressure supplied by the spring bar, Vand this pressure, in turn, is applied to the driven member to maintain the required amount of torque. y By reason of the functioning of the spring bar, the adjustment periods of the clutch assembly are reduced to `a minimum. There are several spring bars on the pressure plate, so that the follow-up `travel of the pressure plate, which is produced by these spring bars, is approximately equal to the deflected length of the spring `bars from their preloaded positions to their fully deec'ted positions. The spring means in the present assembly also performs the function of providing a` yieldable force between the pressure plate and its shifting means for eifecting a cushioned engagement of the clutch drive `and driven members.

The present improvements have been carefully de-` signed and have been successful in preventing the above- Y described objectionable conditions arising in a clutch assembly which is installed in a motor driven vehicle where severe service is encountered while performing heavy work.

Among the primary objects and attainments contemplated by the present improvements are the provision 'of (l) means for creating air lcurrents Within the clutch assembly and causing `these currents to circulate through the clutch assembly to iimp inge upon 4theworking parts whereby aconsiderable portion oftliegeneratedhet in the clutch members is dissipated, (2) means to automatically prevent the tendency of the L overcenter clutch operating mechanism fror'nr unintentionally shifting at high idling speedfrom a position in which the clutch is disengaged Ato a position Where 'said smechanism causes accidental clutch engagement; and( 3) the employment of yieldable springY means, preferably in -the form of a spring bar, which is actedonbythetoggledevices for cushioningithe engagingmovement ofthe pressure plate against the clutch driven plate and also't'o assist inliolding the toggle devices in overente'ripositidns Ywhile'the clutch is engaged.

An object contemplated by th'epresent improvements is to provide definite means Yon certain of lthe rotatable members of the clutch assembly 'for"c'rea.ting `the flow 'of air currents which are drawn rinto the assembly through an axial opening in the backplate or housing and'then be directed between said backplate and the shiftable pressure plate and other parts in radiallyoutward paths so that the coolant air, after impinging upon the clutch parts, is discharged through an annular row of apertures in the backplate or lhousing. Specifically, `this object is attained by providing a plurality of tins extending in generally radial directionson the inner surfaceof the backplate or housing of the assembly, or providing similar iins on the rear surfaceofthe` clutch fpressure plate.

Another object contemplated by the 'presentimprovements resides in providing automatically operable means which `are responsive to centrifugal forces, created at high idling speeds of the assembly when the clutch has been disengaged by the'overcenter devices, said meansbeing edective'to overbalance'a tendency of said overc'enter devices, due to centrifugal forcesacting` thereon, to move out of a clutch `disengaged position, into a position to engage the clutch. This arrangement is `preferably a part of the toggle devicesand tvvhen the clutch has been disengaged by said devices 'while the clutch `is rotating at high idlingspeeds, said centrifugally responsive means is effective to overbalance centrifugal :forces acting on the toggles and thereby maintain the'clutch in disengaged position. The meansfor accomplishing this objectcomi prises a weig'lited'arm eXtendiiigiforwardly from-the toggle device towards the pressure 'plate and is responsive vto centrifugal forces to counteract tlieltendency ofthe toggle device to leave its clutch disengaged position.

The further object contemplated by the present mechanism resides in mounting a leaf spring bar at its end regions on supports on the rear face of the pressure plate and forcibly ytensioning or 'bowing the midregion of this spring bar toward the pressure plate lb'y means of a tensioning device which will lengthen the bar between its end supports. lnthis connection, the toggle devices are arranged to engage the spring bar at its` bowed region so that the `bar will be further elongated between its supports when the 'clutch driving and driven members are engaged. The yieldable action of 'the spring bar is also eifective to maintain the toggle -device in its overcenter position when the clutch parts -have been drivingly engaged.

Additional objects, aims, and advantages of the `improvements contemplated herein will be apparent to persons skilled in the art after the construction and operation of the present clutch assembly is understood from the Within description. lt is preferred to accomplish the foregoing `and `other objects, 'and to ypractice the invention `in substantially the manner hereinafter fully described'and as moreparticu-larlyfpointed out in `the claims, reference being made to the acompanyingfdravfings which fonn apart of this specification. 1 i

In the drawings:

Fig. 1 is vertical elevation showing a rear view of an overcenter heavy duty clutch assembly exemplifying the features contemplated by present improvements;

Fig. 2 is a transverse vertical section of the structure shown in Fig. 1, the View being taken along the plane of line 2--2 thereon;

Fig. 3 is a sectional view of a fragmentary portion of the clutch takenalong the plane of line 3-3 on Fig. l;

Fig. 4 is a schematic view showing details of the bowed spring bar and its manner of operation, the view being taken along the plane of line 4-4 on Fig. l;

Fig. 5 is a fragmentary detail of the overcenter or toggle device in clutch disengaged position with respect to the pressure plate and the spring bar;

Fig. 6 shows a modified arrangement for creating coolant air currents.

The drawings are to be understood as being more or less n of a diagrammatic character for the purpose of disclosing a typical or preferred form of the improvements contemplated herein, and in these drawings like reference charac` ters identify the same parts in the different views.

Figs. l and 2 of the drawings exemplify a typical clutch assembly of the heavyv duty type and show the present improvements incorporated therein. In these views, the flywheel assembly A comprises a flywheel 1t) which is anchored in any suitable manner to the adjacent end of an engine drive shaft or crank shaft 11, and alongside the rear face of this flywheel there is a driven friction disc or plate 12 having a spliued hub 13 for mounting the same for axial movement along the adjacent splined portion of the driven shaft 14. This driven shaft, as seen in Fig. 2, has a reduced end portion 14a which is piloted in antifriction bearings 15 carried by the flywheel, or the drive shaft, as may be desired. The friction disc or plate 12 is adapted to be drivingly engaged against the flywheel face through the medium of an annular pressure plate 16 that is shifted axially by an actuating assembly B which yieldably holds the pressure plate in clutch engaged position against said friction disc. The actuating assembly B has one portion in cooperative association with a backplate or housing assembly C, and it has a second portion which is operably connected to a shift bearing or thrust collar assembly D, the latter assembly being selectively moved manually in forward or rearward directions along the driven shaft 14 for the purpose of effecting the respective engagement or disengagement of the driven friction disc or plate 12 between the ywheel and the pressure plate at the option of the operator or driver of the tractor or other vehicle.

The backplatc assembly C preferably takes the form of a housing 17 having an irregular contour in cross section with an outer peripheral flange 18 which is secured by cap screws 19 to an annular flange 20 extending rearwardly from the outer periphery of the flywheel. The flywheel flange 20 provides an annular recess 10a in the rear face of the flywheel so that the friction plate and pressure plate may be positioned in this recess forwardly of the backplate or housing and thereby reduce the overall axial dimension of the clutch assembly. The pressure plate 16 has a driving connection with the backplate or housing i7 through the instrumentality of rearward or axially extending lugs 2li which are engaged in recesses 22 in adiacent regions of the backplate, thus permitting the pressure plate, housing and flywheel to rotate in unison.

At the central region of the housing, there is an annular flange 23 of generally cylindrical shape which extends axially rearwardly to define a large axial opening 24. The cylindrical flange 23 surrounds the driven shaft 14 and is spaced a considerable distance radially from the said shaft to define an inlet opening for the ingress of extraneous coolant air into the housing when the clutch assembly is in rotation. For the purpose of drawing air into the housing through the opening 24 to impinge upon the clutch members, suitable fins 25 are provided which project forwardly from the inner surface of the housing, and said fins are of an elongate character and extend in generally radial directions on the housing between the axial opening 24 and the annular flange 18 at the outer periphery of the housing. Also, as shown in Fig. 6, fins 25a may be positioned upon the rear surface of the pressure plate which rotates with the backplate or housing, and will thus draw extraneous coolant air into the clutch assembly. Between the axial opening 24 and the outer peripheral flange 18, the housing has therein a plurality of openings 26, which are arranged in an annular row and are each elongated in a circumferential direction as seen in Fig. l. This annular row of apertures 26, define egress or outlet means for discharging the coolant air after it has circulated within the housing and has impinged upon the clutch members in which heat has been generated during operation of the clutch. It will be understood that the coolant airis forcibly drawn into the clutch assembly by means of the fins which function as rotating fan blades, with the result that the temperature of the clutch parts is materially reduced and prevented from becoming overheated, particularly when the clutch is disengaged and may be idling at high speeds.

In addition to the driving lug connection between the pressure plate 16 and the housing or backplate, there are spring reaction connections between these members, each of which comprises a bolt 27 having its head 28 seated in recess 29 on the front face of the pressure plate and has its shank extended through the pressure plate and the housing 18 as shown in Fig. 3. A coiled expansion spring 30 surrounds the outer rearward portion of the bolt with one end engaged with the rear surface of the housing and the other end engaged with an adjusting nut 31 whereby the spring is held under tension. Thus it is apparent that the spring 3i) assists in drawing the pressure plate away from the friction disc when the driving and driven members of the clutch have disengaged.

The actuating assemblies operate to move the pressure plate in one axial direction into contact with the friction disc and press the latter into engagement with the adjacent flywheel face as shown in 2, and these actuating assemblies when moved in another direction become effective to release the clutch in the manner shown in Fig. r5. Since all of the assemblies B are identical, one description thereof will suffice. The assembly preferably takes the form of a toggle which comprises the Siamese links 32 which are arranged in a generally upstanding position and are pivotally connected at their lower regions by a pin 33 to an annular boss 34 formed as a part of the shift bearing or thrust collar assembly D. Fig. 2 shows the assembly D as comprising an axially elongate sleeve 35 on driven shaft 1d with an annular boss 3dat its forward end and having a collar 3d surrounding its rear region with antifriction bearings 37 interposed between said sleeve and collar. The usual shift fori; (not shown) engages the collar 36 for moving the thrust bearing assembly D longitudinally on the driven shaft l@ to operate the toggle of the clutch actuating assembly D. The outer surface of the annularaxial flange 23 of the housing is threaded to receive a take-up ring 35i of l..-shapc in cross section which is similarly threaded on the inner surface of its axial flange, whereby the ring 38 may be rotatably adjusted on its support. Mounted in the angle formed by the L-shaped flanges of the ring, there is an annulus-39 which is arranged with one face abutting the radial flange of the ring and is held in place by a spring snap ring device 4d which contacts the opposite face of said annulus. The second member of the overcenter toggle comprises an arm i1 extending in a generally horizontal direction with its rearward end coupled to the adjacent end of the Siamese links 32 by a pin d2, and thc forward end of link 4l is pivotally connected to the annulus by a pin 43 extending between a pair of ears 44 on the annulus. A second arm 45 extends forwardly of the pin 43 towards the pressure plate 16 and is provided with a weight 46 on its freeendssothat the arm `4S isresponsive `to centrifugal forces created by the rotation of the clutch assembly.

.In operation, `when .the shift collar assembly D is moved to the right from the position shown in .Fig 2, the actuating assembly assumes `the position shown in Fig. .5 Vso `that the toggle, comprising links 32 and arm 41, `assume a somewhat liattened position and the clutch is disengaged. In the event the clutch may be rotating at high idlingspeeds, the knuckle portion of the toggle device at the `pin `42 has the `tendency `to move radially outward `to -a position where the arrangement is likely to effect unintentional clutch engagement or at least move the `clutch members close enough to each `other as to create a .drag `on `the friction .members This tendency of the toggle to unintentionally `engage the clutch parts is definitely avoided byreason of the fact that the weighted arm 45 `overbalances the centrifugal forces which have been exerted on the toggle.

The connection between the pressure plate 16 and the toggle assembly B preferably takes the form of a cam member 4.7 on the hub region of the arm A41 adjacent the pivotpin 43 andis arranged with its toe projecting toward the pressure plate. In View of the fact that heavy duty friction discs are of a simplified type without cushioningr means between the facings and the intermediate plate thereof, it is desirable, though not essential, to Vprovide means for cushioning clutch packingl pressure when the clutch is .being engaged. 'In the present arrangement, a cushioning elfect is acquired by providing spring means between the pressure plate and the toggle, said means being preferably in the form of a spring metal bar 455. This spring bar 48, as shown on Fig. 1, is of elongate form and is mounted at its end regions on supports 49 on the rear of the pressure plate so that said spring `bar extends in a direction `generally transverse t-o the plane of the toggle assembly B. Suitable clips SQ hold the bar on its supports and `said bar is forcibly held in a bowed state between its ends by means of a Iheavy retainer member or `bracket member 51, which is anchored to the pressure plate 'by a` cap screw 52. The supports 49 at the ends of thespringbars 48 are located on the mean radius of the rear face of the pressure plate, which is between the `inner and outer peripheries of said plate, so that even pressure is produced on the friction surfaces of Vthe driven disc member. Thus distorted or uneven conditions are prevented on the surfaces when there is wear on 'the driving and driven members of the assembly. The spring `hars are deflected to stops 49a on the rear surface of tire pressure plate intermediate the supports 49, and these stops allow the clutch to be adjusted beyond its rated torque capacity without injury tothe spring ba-rs. After an overload of pressure, that has been applied to the pressure plate, is decreased and `is equal to the pressure produced by the fully deflected spring bars, the pressure of the fully deflected spring bars is applied to the driven disc member. The initial amount of deflection of the spring bar is `not suicient to produce any appreciable amount of pressure required to `operate the clutch to its torque capacity. Therefore, the spring bar is preloaded or trapped at a specific height, and it is `from this preloaded height position to `the fully deected position fof the spring bar that sufficient pressure is produced to operate the clutch at its specified torque. The trapped or preloaded condition of the spring bar eliminates the requirement of having a larger releasesleeve travel to obtain ample pressure plate releasel travel.

The bowed midregion of the spring `bar 4S is adapted to :be `engaged bythe toe of cam 47 during the operation of engaging the clutch members. When the thrust collar is moved in a forward direction '(to the left in Fig. 2) the cam 47will increase the bow of the spring bar 48 and thereby the spring bar is `lengthened between its supports. rl`his is schematically shown in detail in Fig. 4 wherein itlis to benotedthatthetfulllinesshowthe springbar 48 finritsnormal rbowed state, and .the 'dotted lines show bowed-elfect resulting from `the engagement of the cam 47 with the midregion of said bar. Whenthe clutchtis inengaged-position, `the toggle is in overcenter position as in Fig. 2, :so .that .the spring tension `of the vbar 48 is exerted against the cam 47 andtendsto swing the knuckle portionrof the toggle `inta downward direction to effectively Ymaintain the toggle against any attening movement thereof. In other words, the spring bar 48 is capable of performing the above-described dual functions. Furthermore, when the toggle assembly -B is moved towards either clutch `engaged or disengagedpositiom `the toggle assembly `will pass `from one side to .the other of the overcenter positionwith a snap action, and` this overcenter snapping action is 'eifectivelytcushioned by the spring bar.

As previously exp1ained,.the take-up ring 38 isscrewed on the exterior surface of the ange 23%, and since the toggle .iarrangementis carried by this take-up ring through themedium of the annulus 39, saidring may .be rotated inone direction or the other to bodily movethe assembly toward or away `from the pressure plate 16 as desired. The take-up ring is locked in its selected positions by means Yof a latch assembly 53 that is hingedly mounted betweenears b on a rear portion of the housing by means of a pivot 54 and is `provided 'with an arm 55 projecting radially inward to engage in one of the notches 56 made in the edge or outerperiphery'of the take-up ring 38. .A spring 57 #of approximately U-shape is effective to hold the latch device in its engaged `position with respect to the notches 56.

From the foregoing description it is apparent that the arms 41 and 45 define a rock lever `or bell-crank member which =is fulcrurned intermediate its ends on the pivot pin 43, and also Vthat the cam member 47 provides what may .be termed a third or auxiliary arm of the bell-crank. When cam f47 acts upon the spring bar 48, there is a cushioning of the ,force which is being `applied to the pressure plate :by the `toggle device during movement of the clutch members into `clutch engaged positions. This spring bar is effective to assist in holding the toggle members in` overcenter positions during clutch engagement. 4Also `certain `portions of `the `clutch assembly have air circulating .tins which produce air `currents `to reduce the temperature of the working parts of the clutch.

While the present structure has been described in detailin a typical or preferred form or embodiment, it will be apparent to persons skilled in the art, after understanding the construction and voperation of the improvements contemplated herein that various changes and ymodi- `cations thereof may be made without departing from `the spirit or scope thereof. It is contemplated in the appended claims yto cover all such changes and modifications.

Wh'at is claimed is:

1. A clutch assembly comprising a driving member.; .an :axially shiftable pressure plate; clutch operating lever `means pivotally carried by said driving member; means for applying pressure to said lever .means to effect clutch engagement; cireumferentially spaced supports on `the rear face of said pressure plate; and a springmetalsbar carried at 4its ends by said supports in spaced relation'to said pressure plate and forcibly held in a bowed condition respecting said pressure plate, said bar being engageable `adjacent its mid-region by said lever means to `in- -crease the length of said bar between said supports thereby to impart clutch engaging `pressure to said pressure plate.

.2. A clutch assembly comprising a driving member; an axially .shiftable pressure plate member; clutch lever means pivotally carried by said driving member; means for applying pressure to said lever means to effect clutch engagement; a spring `metal bar arranged parallel to aplane tangent -to said pressure plate member and supported/adjacent itsends in spaced relation to said pressure plate member; and means engaged with the mid-region of said bar in constantly preloaded condition for forcibly bowing said bar towards said pressure plate member, said preloaded bowed region of said bar being engaged by said lever means to increase its length between its supports and thereby impart yielding clutch engaging pressure to said pressure plate member.

3. A clutch comprising a rotatable driving member; a shiftable pressure plate member rotatable with said driving member; a driven clutch plate arranged for frictional engagement between said members; a back plate carried by said driving member and having a portion rearward of said pressure plate member; clutch operating lever means pivotally mounted on said back plate for shifting said pressure plate member; means for applying clutch packing pressure to said lever means for axially moving said pressure plate member to effect clutch engagement; and Van elongate straight metal bar supported at its end regions in spaced relation to said pressure plate member and having a region intermediate its ends constantly bowed with respect to said pressure plate member, said bar engaged at its bowed region by said lever means and being effective upon application of pressure by said lever means to reduce the radius of the are of said bowed re gion of the bar and cause frictional engagement of said driven clutch plate by said members.

4. A clutch comprising a rotatable driving member; a shiftable pressure plate member rotatable with said driving member; a driven clutch plate arranged for frictional engagement between said members; a back plate rearward of said pressure plate member and carried by said driving member; clutch operating lever means pivotally mounted on said back plate for operating said pressure plate member; means for applying clutch packing pressure to said lever means for shifting said pressure plate member to` effect clutch engagement; an elongate leaf spring supported at its end regions on said pressure plate member in spaced relation thereto; and means engaged with said spring intermediate the ends thereof for holding said spring in a constantly bowed condition with respect to said pressure plate member, said lever means engaging the bowed region of said spring and being effective to vary the radius of the arc of said bowed region and engage said clutcb upon application of pressure by said lever means.

5. A clutch comprising a rotatable driving member; a shiftable pressure plate member rotatable with said driving member; a driven clutch plate arranged for frictional engagement between said members; clutch operating cam means pivotally supported by said driving member; means for applying clutch packing pressure to said cam means for shifting said pressure plate member to effect clutch engagement; an elongate yieldable metal bar supported at its end regions in spaced relation to said pressure plate member; and restraining means engaged with the intermediate region of said bar for constantly holding said bar in a condition bowed towards said pressure plate member, said cam means engaging said bowed region of said bar and being effective upon application of pressure to said cam means to elfect further bowing of said bar towards said pressure plate member.

6. A clutch assembly comprising a rotatable driving member; an axially shiftable pressure plate member rotatable with said driving member; a driven clutch plate arranged for frictional engagement between said members; a back plate carried by driving member; a rock lever pivoted intermediate its ends on said back plate and having forward and rearward extending arms; means for applying clutch packing pressure to the rearward extending arm of said rock lever; and a yieldable metal bar supported at its end regions in spaced relation to said pressure plate member and having a region intermediate its ends constantly maintained in bowed condition with respect to said pressure plate member, said bar being engaged at said 'bowed region by the forward extending arm of said rock lever and being operable upon application of pressure by the rearward extending arm of said rock lever to elongate the portion of the bar between its supports thereby to reduce the radius of curvature of said bowed region and eifect frictional engagement of said driven clutch plate between said members.

7. A clutch assembly comprising a rotatable driving member; an axially shiftable pressure plate member rotatable with said driving member; a driven clutch plate arranged for frictional engagement between said members; a back plate carried by said driving member; an axially movable pressure exerting member rearward of said back plate; an overcenter toggle device carried by said back plate, a iirst portion of said toggle device extending towards said pressure plate member, and a second portion of said toggle device having operative connection with said pressure exerting member; and a spring metal bar supported at its end regions on said pressure plate member in spaced relation thereto and having a region intermediate its ends which is characterized by a preloaded bow extending towards said pressure plate member, said bar being engaged at said bowed region by said first portion of the toggle device, and being effective upon application of pressure by said movable pressure exerting member to alter the radius of curvature of said bowed region and thereby frictionally engage said driven clutch plate between said driving and pressure plate members.

8. A clutch comprising a rotatable driving member; an axially shiftable pressure plate member rotatable with said driving member; a driven clutch plate arranged for frictional engagement between said members; a back plate carried by driving member; a rock lever pivoted intermediate its ends on said back plate and having forward and rearward extending arms; means for applying clutch packing pressure to the rearward extending arm of said rock lever; and a metal bar supported at its end regions-on said pressure plate member in spaced relation thereto and having a region intermediate its ends preloaded in a bowed condition with respect to said pressure plate member, said bar being engaged at said bowed region by the forward extending arm of said rock lever and being operable upon application of pressure by the rearward extending arm of said rock lever to reduce the radius of curvature of said bowed region and effect frictional engagement of said driven clutch plate by said members.

9. In a clutch assembly which comprises a rotatable driving member; an axially shiftable pressure plate rotatable with said driving member; a driven clutch plate arranged for frictional engagement between said driving member and pressure plate; a back plate carried by driving member; and an axially shiftable member rearward of said back plate; those improvements which comprise a spring metal bar supported at its end regions on said pressure plate and being pretensioned in a bow which extends toward said pressure plate in 4non-contacting relation thereto; means for forcibly holding said spring bar in its pretensioned bowed condition; a rock lever fulcrumed intermediate its ends on said back plate; and a link operatively connecting said rock lever to said axially shiftable member, said rock lever and said link defining an overeenter toggle device; a first arm of said rock lever having a cam portion engageable with the bowed region of said spring metal bar, and a second arm of said rock lever having a weight at its end remote to the lever fulcrum for imparting centrifugal forces to the rock lever, said rst arm and said link at high idling speed having a tendency in response to centrifugal forces to assume a position to engage the clutch assembly, and said weight in response to centrifugal forces being effective to overbalance said tendency and to maintain said first arm and said link in clutch disengaging position.

l0. A clutch comprising a rotatable driving member; a shiftable pressure plate member rotatable with said driving member; a driven clutch plate arranged for frictional engagement between said members; a baci; plate carried by said driving member and having a portion rearward of said pressure plate member; :1 plurality of overcenter toggle devices pivotally mounted on said back plate and being operable to shift said pressure plate member into clutch engaged position; means for moving said toggle devices to forward and rearward overcenter positions during which snap actions occur when passing dead center; and elongate spring metal yieldable bars supported at their end regions on said pressure plate member in spaced relation thereto and pretensioncd toward said pressure plate member, said pretensioned spring bars being engageable intermediate their ends by said toggle devices, said spring bars being effective to cushion the aforesaid snap actions of said toggle devices when said devices move past their respective dead centers.

11. A clutch comprising axially spaced rotatable driving members, one of which defines a shiftable pressure plate; a driven clutch plate arranged for frictional engagement between said members; a back plate rotatable with said driving members; an overcenter toggle device pivotally mounted on said back plate for shifting said pressure plate, said toggle device being movable past its dead center by a snap action; and an elongate spring metal bar supported at its end regions in spaced relation to said pressure plate and being pretensioned in a bow toward said pressure plate, said spring bar being engaged at its mid-region by an adjacent member of said toggle device to effect further bowing of said spring bar, said spring bar imparting a cushioning effect to the aforesaid snap action of the toggle during operation of the latter.

12. A clutch comprising driving and driven members, said driven member being defined by an axially shiftable annular pressure plate; a spring metal bar supported adjacent its end regions at the mean radius of said pressure plate between the inner and outer peripheries thereof, said spring bar being preloaded in a bow extending toward said pressure plate in an arc having a predetermined selected radius; clutch operating lever means pivotally carried by said driving member and being operable to engage the mid-region of said spring bar and force it toward said pressure plate thereby to reduce the radius of the arc of the bowed region and increase the lenght of the spring bar between its said supports; and means for applying pressure to said lever means to eilect the aforesaid operation thereof and the engagement of said clutch members. i

10 13. A clutch comprising driving and driven members, driven member being dened by an axially shiftable annular pressure plate; spaced supports on said pressure plate at the mean radius thereof between the inner and outer peripheries thereof; a spring metal bar carried by said supports and being preloaded in a bow extending toward said pressure plate in an arc having a predetermined radius; a clutch operating lever on said driving member and being operable to engage the mid-region of said spring bar and force it toward said pressure plate thereby to reduce the radius of the arc of the bowed region and increase the length of the spring bar between its said supports; and means for applying pressure to said lever means lo effect the aforesaid operation thereof to engage said clutch members.

14. A clutch comprising driving and driven members, Y

said driven member being defined by an axially shiftable annular pressure plate; spaced supports on said pressure plate at the mean radius thereof between the inner and outer peripheries; a spring metal bar carried at its ends by said supports in spaced relation to said pressure plate; means on said pressure plate engaged with said spring bar intermediate its ends `for preloading said bar in a bow extending toward said pressure plate in an arc of predetermined radius; a clutch actuating lever on said driving member and operable against the mid-region of said spring bar to force said region toward said pressure plate thereby to reduce the radius of the arc and increase the length of the spring bar between its said supports; and means for applying pressure to said lever to effect the aforesaid operation thereof to engage said clutch members.

References Cited in the tile of this patent UNITED STATES PATENTS 1,411,110 Livermore Mar. 28, 1922 1,475,909 Wasserman Nov. 27, 1923 1,572,370 Smith Feb. 9, 1926 1,913,944 Morin June 13, 1933 1,915,732 Goldschmidt `lune 27, 1933 2,115,763 Burke May 3, 1938 2,251,366 Miller et al. Aug. 5, 1941 2,300,187 Wemp Oct. 27, 1942 2,348,025 Peets et al. May 2, 1944 2,370,360 McLean et al. Feb. 27, 1945 2,523,501 Davies et al Sept. 26, 1950 

